(CNN) - A stone monument in Rex, Georgia, celebrating first lady Michelle Obama's great-great-great grandmother Melvinia Shields was knocked over from its pedestal onto a concrete slab Saturday night.
"It was done purposely. If I had to speculate some people may think it was a prank; not realizing what a serious matter it is. I really believe we have gone beyond any other motives," Clayton County Commissioner Sonna Singleton told CNN Tuesday during a phone conversation.
Clayton County has an open investigation into the incident, but has no leads, Singleton said.
A new monument was expected to be installed Tuesday, almost a year after the original stone was erected on June 26, 2012.
Born into slavery, Melvinia Shields was listed on an 1870 census document as a farm laborer, washwoman and maid, according to a historical website run by the State of Georgia. She was later described as a midwife.
After a New York Times article linked Shields to Michelle Obama in 2009, the town of Rex decided to dedicate a monument in her honor. The now-annual Melvinia Shields celebration is slated to take place later this month.